Laser machining systems and methods are commonly used to machine various types of materials and structures. Such laser machining systems and methods may provide a number of advantages including lower manufacturing costs, increased throughput and production yield, and improved quality. In the area of solar panels, for example, the advantages of laser machining could significantly enhance the efficiency and viability of solar energy technology.
In the manufacture of thin film photovoltaic (PV) solar panels, laser machining techniques may be used to scribe the various thin film layers in a panel to form electrically connected cells. In one type of PV solar panel, three layers are deposited to form the panel and lines are scribed after each new deposition. The area on the panel including these lines is considered a wasted area that does not contribute to solar energy conversion. Thus, the lines should be straight and aligned accurately to minimize this wasted area and to provide the best efficiency. High scribing speeds and increased throughput are also desirable. Providing accurate high speed scribing of thin film PV solar panels (and other similar structures) presents a number of unique challenges.
Large area workpieces, such as solar panels, may have variations in thickness and/or surface flatness and may have coating non-uniformities over the relatively large area, which may adversely affect machining of the workpiece. In particular, variations in the flatness of the workpiece may result in variations in the process distance from a beam delivery system, which causes changes in focus or demagnification of the laser on the workpiece. Variations in surface flatness and thickness and coating non-uniformities over relatively large processing distances may result in undesirable scribe variations such as variations in width, depth, fluence, heat-affected-zones and penetration, which can adversely affect the precision of the scribes. The relatively large scribing distance also increases the chances of errors in the scribe position and orientation on a large area workpiece.
Another challenge with laser machining of PV solar panels is the ability to maintain accuracy with the long working distance from the laser source to the workpiece. Angular pointing instability may result from the long working distance and longer beam delivery path. When the laser beam must travel longer distances to the workpiece and far-field scribing techniques are used, for example, the position of the laser spot focused on the workpiece can vary due to laser pointing variations, resulting in inaccuracies in line straightness and alignment.